The overall goal of the Phase I project is to demonstrate the feasibility of producing CdZnTe detector arrays having a p-i-n structure with performance superior to similar arrays with m-s-m structure. These arrays are intended as building blocks of a SPECT system. During the Phase I project, both CdS and In will be evaluated as the n layers for a p-i-n structure, and based on the results one will be selected for the final design. Experimental procedures will be established for deposition of these layers, annealing them and finally, segmenting them for array fabrication. Extensive testing of these devices will be carried out by measuring their dark current, electrical noise, spectral resolution and efficiency. The arrays will then be sent to UCSF where they will be mounted on an existing SPECT-CT gantry and connected to their fast pulse (50 ns shaping) processing electronics which collects data for both SPECT and CT in pulse mode. Imaging studies will be conducted using phantoms available at UCSF.